TWI405502B - Dimmer circuit of light emitted diode and isolated voltage generator and dimmer method thereof - Google Patents

Abstract

An isolated configuration dimmer circuit of a light emitting diode (LED) applied to a conventional triac dimmer and a dimmer method are provided. When a dimmer phase angle of the triac dimmer is regulated, a second side winding of a transformer of the isolated configuration produces a pulse width corresponding to a modulated alternating current (AC) voltage, so as to regulate the pulse width of a driving signal output by the second side winding of the transformer. In addition, the dimmer circuit regulates the magnitude of a current flowing through the light emitting diode (LED) according to the pulse width corresponding to the modulated AC voltage. Accordingly, the dimmer circuit regulates the pulse width and the magnitude of the current flowing through the LED according to the dimmer phase angle of the triac dimmer. Therefore, a dimmer range of the LED can be increased.

Description

Dimming circuit of light-emitting diode and its isolated voltage generator Light method

The present invention relates to a dimming circuit, and more particularly to a dimming circuit for a light emitting diode and an isolated voltage generator and dimming method thereof.

Light Emitting Diode (LED) is small, power-saving and durable, and as the process matures, the price drops. Recently, products using light-emitting diodes as light sources are becoming more and more popular. In addition, the light-emitting diode has a low operating voltage (only 1.5-3V), can actively emit light and has a certain brightness, and the brightness can be adjusted by voltage or current, and has the characteristics of impact resistance, vibration resistance and long life (100,000 hours). Light-emitting diodes are widely used in a variety of terminal equipment, from automotive headlights, traffic lights, text displays, billboards and large-screen video displays, to general-purpose architectural lighting and LCD backlighting.

FIG. 1A is a schematic diagram of a system of a dimming circuit of a conventional light emitting diode. Referring to FIG. 1A, the dimming circuit 100 is a basic circuit for the buck constant current control chip LM3445 applied to the dimming of the LED, and the detailed circuit operation of the dimming circuit 100 can be referred to the description of the LM3445 technical manual. In the dimming circuit 100, the AC signal VAC is first modulated by a phase dimmer (TRIAC DIMMER) according to its dimming angle, and then the pulse width detecting circuit 110 is used to modulate the modulated signal after the phase dimmer is modulated. Take out the Vac. Then, the pulse of the modulation signal Vac is further passed through the low-pass filter circuit 120. The wave width is converted to a DC voltage. The wafer LM3445 controls the switching signal of the transistor 130 according to the DC voltage to control the current of the load current ILED driving the LED.

FIG. 1B is a waveform diagram of the modulation signal and the load current of FIG. 1A. Referring to FIG. 1A and FIG. 1B, when the dimming angle of the phase dimmer is increased, the pulse width of the modulation signal Vac is relatively narrowed. When the pulse width of the modulation signal Vac is narrowed, the DC voltage received by the wafer LM3445 is relatively lowered. At this time, the wafer LM3445 controls the transistor 130 to reduce the current of the load current ILED, and the luminance of the light-emitting diode becomes dark as the current of the load current ILED decreases.

According to the circuit shown in FIG. 1A, the grounding points of the dimming circuit 100 are all the same grounding point, that is, the dimming circuit 100 is an un-isolated dimming circuit. In addition, the way in which the dimming circuit 100 performs dimming is to adjust the current magnitude of the load current ILED.

The present invention provides an isolated voltage generator that generates a pulse width corresponding to a modulated alternating voltage through a secondary side of a transformer to correspondingly adjust a pulse width of a drive signal outputted by a secondary side of the transformer.

The invention provides a dimming circuit for a light emitting diode and a dimming method thereof for adjusting a pulse width of a current flowing through the light emitting diode according to a dimming phase angle. In addition, the current of the current flowing through the light emitting diode can be adjusted according to the dimming phase angle.

The invention provides an isolated voltage generator suitable for emitting diodes A body modulating circuit, wherein the illuminating diode driving circuit has a phase dimmer bit. The isolated voltage generator includes a rectifier, a controller, a transformer, a switch, a voltage divider, and a first resistor. The rectifier receives a first voltage modulated by the phase dimmer. The controller has an input end, a drive output end, a feedback end, and a current detecting end. The controller generates a control signal according to the voltage received by the feedback terminal and the current detecting terminal, and outputs a control signal by the driving output terminal. The transformer has a primary side, a secondary side and a tertiary side, wherein the first end of the primary side is coupled to the rectifier, the first end of the secondary side outputs a driving signal, and the second end of the secondary side is coupled to the second grounding voltage, the third side The input is coupled between the input end of the controller and the first ground voltage. The switch has a control end, a first end and a second end, and the control end of the switch is coupled to the drive output end of the controller, the first end of the switch is coupled to the second end of the primary side, and the second end of the switch is coupled to the controller Current detection terminal. The voltage divider is coupled between the first end of the tertiary side of the transformer, the feedback end of the controller, and the first ground voltage to provide a voltage divider to the feedback end of the controller. The first resistor is coupled between the current detecting end of the controller and the first ground voltage.

The invention further provides a dimming circuit for a light emitting diode, comprising a phase dimmer, an isolated voltage generator, and a current controller. The phase dimmer receives the first voltage for modulating the first voltage according to the dimming phase angle. The isolated voltage generator is coupled to the phase dimmer to generate a driving signal according to the modulated first voltage to drive the at least one light emitting diode, wherein the first voltage is isolated from the voltage forming the driving signal. The current controller controls the current flowing through the light emitting diode according to the adjustment signal.

The invention further provides a dimming method for a light emitting diode, which is suitable for a dimming circuit of a light emitting diode, and a phase dimming of a dimming circuit of the light emitting diode The device is configured to modulate an alternating voltage according to a dimming phase angle, and the isolated voltage generator of the dimming circuit of the light emitting diode generates a driving signal according to the modulated alternating voltage to drive at least one light emitting diode, the light emitting diode A current controller of the body dimming circuit controls current flow through the light emitting diode. In the dimming method, when the dimming phase angle is lowered, the pulse width of the modulated alternating voltage is increased, and the pulse width of the driving signal is correspondingly increased to increase the flow through the light emitting diode. The pulse width of the current in which the voltage forming the modulated alternating voltage is isolated from the voltage forming the drive signal. When the dimming phase angle is increased, the pulse width of the modulated alternating voltage is reduced, and the pulse width of the drive signal is correspondingly reduced to reduce the pulse width of the current flowing through the light emitting diode.

Based on the above, the isolated voltage generator of the present invention transmits the pulse width of the modulated signal through the transformer having three sides, and adjusts the pulse width of the driving signal and the current of the driving signal according to the pulse width of the modulated signal. . The dimming circuit of the light-emitting diode of the present invention and the dimming method thereof adjust the pulse width and current of the current flowing through the series of the light-emitting diodes according to the dimming phase angle of the phase dimmer. Thereby, the range of dimming of the light emitting diode can be increased.

The above described features and advantages of the present invention will be more apparent from the following description.

2A is a schematic diagram of a system of a dimming circuit according to an embodiment of the invention. Referring to FIG. 2A, the dimming circuit 200 includes a phase dimmer 210 and an isolated type. The voltage generator 220 and the current controller 230, wherein the dimming circuit 200 is assumed to drive the light emitting diode and perform dimming. The phase dimmer 210 receives the AC voltage VAC to adjust the AC voltage VAC according to the dimming phase angle thereof, thereby adjusting the pulse width of the modulated AC voltage VAC according to the dimming phase angle. The modulated AC voltage VAC is referred to as a modulation signal Vac, wherein the AC voltage VAC can be a commercial AC voltage.

The isolated voltage generator 220 is coupled to the phase dimmer 210 to generate the driving signal Vo according to the modulation signal Vac to drive the LED array 50. The LED array 50 is a schematic diagram, but the actual The upper LED array 50 may include at least one light emitting diode, that is, the light emitting diode series 50 and may be one or two or more light emitting diodes. It should be noted that the voltages forming the modulation signal Vac and the driving signal Vo are isolated from each other, that is, the current loop forming the modulation signal Vac has no common path with the current loop forming the driving signal Vo. Moreover, the isolated voltage generator 220 can be a flyback architecture or a forward architecture, and the architecture is selected according to the current magnitude of the driving signal Vo and the components used. The current controller 230 controls the magnitude of the current flowing through the LED array 50 according to the adjustment signal Dim, wherein the current controller 230 can utilize a buck converter, a boost converter, or a buck-boost converter. The Buck-Boost converter is implemented, and according to the type of the current controller 230, the adjustment signal Dim may be a DC voltage or a pulse signal.

2B is a circuit diagram of the dimming circuit of FIG. 2A. Please refer to FIG. 2B. In this embodiment, the isolated voltage generator 220 includes a rectifier 221, a controller 222, a transformer TR1, capacitors C1, C2, C3, and C4, resistors R1, R2, R3, and R4, and diodes D1, D2, and D3. Transistor M1. The rectifier 221 receives the modulated signal Vac to rectify the modulated signal Vac into a modulated signal Vac'. The rectifier 221 is exemplified herein as a bridge rectifier, but is not limited thereto in other embodiments.

The capacitor C1 is coupled between the rectifier 221 and the first ground voltage. The resistor R1 is coupled between the rectifier 221 and the input terminal VIN of the controller 222. The capacitor C2 is coupled between the input terminal VIN of the controller 222 and the first ground voltage. The diode D1 is coupled between the first end 225a of the tertiary side 225 of the transformer TR1 and the input terminal VIN of the controller 222. The second end 225b of the tertiary side 225 of the transformer TR1 is coupled to the first ground voltage. The diode D2 is coupled between the first end 225a of the tertiary side 225 of the transformer TR1 and the resistor R2.

The capacitor C3 is coupled between the first end 225a of the tertiary side 225 of the transformer TR1 and the first ground voltage. The resistor R2 is coupled between the first end 225a of the tertiary side 225 of the transformer TR1 and the feedback end Fb of the controller 222. The resistor R3 is coupled between the feedback terminal Fb of the controller 222 and the first ground voltage. The circuit operation of the resistors R2 and R3 can be regarded as a voltage divider for dividing the voltage of the third side of the transformer TR1 to provide a voltage division to the feedback terminal Fb of the controller 222.

The first end 223a of the primary side 223 of the transformer TR1 is coupled to the rectifier 221. The drain (ie, the first end) of the transistor M1 is coupled to the second end 223b of the primary side 223 of the transformer TR1, and the source of the transistor M1 (ie, the first The two ends are coupled to the current detecting terminal Cs of the controller 222. The gate (ie, the control terminal) of the transistor M1 is coupled to the driving output terminal NDRV of the controller 222, wherein the transistor M1 is here a metal oxygen half (metal) The -oxide-semiconductor, MOS) field effect transistor is taken as an example, and the transistor M1 can be regarded as a switch in the circuit. The resistor R4 is coupled between the current detecting terminal Cs connected to the controller 222 and the first ground voltage.

The first end 224a of the secondary side 224 of the transformer TR1 is coupled to the anode of the diode D3, and the second end 224b of the secondary side 224 of the transformer TR1 is coupled to the second ground voltage. The cathode of the diode D3 is coupled to the LED array 50. The capacitor C4 is coupled between the cathode of the diode D3 and the second ground voltage. The controller 222 determines whether to operate according to the voltage received by the input terminal VIN, and generates a control signal according to the voltage received by the feedback terminal Fb and the current detecting terminal Cs, and drives the output terminal NDRV to output a control signal to the power. The gate of the crystal M1 controls whether the transistor M1 is turned on. Capacitors C1~C3 are used for filtering in the circuit, and capacitor C4 can be a capacitor of a large capacitance value to regulate the driving signal Vo.

2C is a waveform diagram of the modulation signal Vac', the driving signal Vo, and the current i _L of the dimming circuit of FIG. 2B. Referring to FIG. 2B and FIG. 2C, when the modulation signal Vac' forms a pulse wave, the input terminal VIN of the controller 222 receives the voltage through the resistor R1 and starts to operate. At this time, the pulse wave of the modulation signal Vac' is also fed back to the feedback terminal Fb of the controller 222 through the tertiary side 225 of the transformer TR1, and the controller 222 receives the voltage at the feedback terminal Fb and the controller 222 will The control voltage is detected and generated according to the voltage of the current detecting terminal Cs to control the on-time of the transistor M1. In other words, when the voltage received by the feedback terminal Fb increases, the voltage of the current detecting terminal Cs decreases, and the controller 222 reduces the conduction time of the transistor M1 through the feedback mechanism to make the current flowing through the primary side 223. If the voltage of the feedback terminal Fb drops, the voltage of the current detecting terminal Cs will increase, and the controller 222 will increase the conduction time of the transistor M1 through the control feedback mechanism to make the flow through the primary side 223. As the current increases, the voltage at the feedback terminal Fb will increase again to reach equilibrium. Therefore, the current flowing through the primary side 223 of the transformer TR1 is substantially maintained at a constant value due to the influence of the transistor M1. Therefore, the energy transmitted through the coil of the transformer TR1 is maintained constant, and the voltage of the drive signal Vo is substantially maintained. A voltage value.

When the modulation signal Vac' is not formed with a pulse wave, no current flows through the primary side 223 of the transformer TR1, that is, the coil of the transformer TR1 does not transmit energy, causing the feedback terminal Fb of the controller 222 to receive no voltage. . At this time, the control voltage generated by the controller 222 controls the on-time of the transistor M1 to increase. Also, the voltage of the drive signal Vo approaches the second ground voltage. According to the above, the voltage of the driving signal Vo is maintained at a voltage value when the modulated signal Vac' forms a pulse wave, and is maintained close to the second ground voltage when the modulated signal Vac' does not form a pulse wave, that is, the driving signal Vo A pulse wave is formed according to the modulation signal Vac', and the pulse width of the drive signal Vo is close to the pulse width of the modulation signal Vac'.

Since the modulation signal Vac' is the AC voltage VAC, it is modulated by the phase dimmer 210 and rectified by the rectifier 221. Therefore, when the dimming phase angle of the phase dimmer 210 is increased, the on-time of the phase dimmer 210 is shortened, and the pulse width of the modulation signal Vac' is narrowed, and the pulse wave of the driving signal Vo is driven. The width will be correspondingly narrowed, wherein the adjustment of the dimming phase angle of the phase dimmer 210 will be described later. When the pulse width of the drive signal Vo is narrowed, the pulse width of the current i _L flowing through the LED array 50 is also narrowed. Therefore, the average current flowing through the light-emitting diode series 50 is lowered, so that the luminance of the light-emitting diode series 50 is darkened.

2D is a waveform diagram of the modulation signal Vac', the driving signal Vo, and the current i _L of the dimming circuit of FIG. 2B. Referring to FIG. 2C and FIG. 2D, when the dimming phase angle of the phase dimmer 210 is lowered, the on-time of the phase dimmer 210 is increased, and the pulse width of the modulation signal Vac' is widened, and The pulse width of the drive signal Vo is correspondingly widened. When the pulse width of the drive signal Vo is widened, the pulse width of the current i _L flowing through the LED array 50 is also widened. Therefore, the average current flowing through the light-emitting diode series 50 is increased, so that the luminance of the light-emitting diode series 50 is brightened.

The controller 222 can be implemented by stepping down the constant current control chip MAX16801. The input terminal VIN of the controller 222 corresponds to the pin IN of the chip MAX16801, and the driving output terminal NDRV of the controller 222 corresponds to the NDRV pin of the chip. The controller 222 The feedback terminal Fb corresponds to the pin of the wafer DIM/Fb, and the current detecting terminal Cs of the controller 222 corresponds to the pin of the wafer Cs.

2E is a circuit diagram of the phase dimmer of FIG. 2B. Referring to FIG. 2E, the phase dimmer 210 includes a resistor R5, a capacitor C5, a diode for alternating current (DIAC) 211, and a Tri-electrode AC switch (TRIAC) 212. When capacitor C5 When the voltage reaches the threshold value of the trigger bidirectional trigger diode 211, the bidirectional trigger diode 211 is turned on, so that the three-pole AC switch 212 receives the voltage and is turned on. Since capacitor C5 is connected in series with resistor R5, the speed at which the capacitor is charged is determined by the RC constant of capacitor C5 and resistor R5. In other words, the higher the resistance of the resistor R5, the longer the capacitor C5 is charged to the critical value, that is, the higher the phase of the three-pole AC switch 212 is turned on, so that the on-time of the three-pole AC switch 212 becomes shorter; The lower the resistance of the resistor R5, the shorter the time during which the capacitor C5 is charged to the critical value, that is, the lower the phase at which the three-pole AC switch 212 is turned on, so that the on-time of the three-pole AC switch 212 becomes longer. Therefore, by adjusting the resistance of the resistor R5, the phase of the conduction of the three-pole AC switch 212 can be adjusted, and the dimming phase angle of the phase dimmer 210 can be adjusted.

2F is a circuit diagram of the current controller of FIG. 2B coupled to the LED array. Referring to FIG. 2F, in the embodiment, the current controller 230 takes a buck converter as an example, and the adjustment signal Dim is assumed to be a DC voltage. The current controller 230 includes a voltage controller 231, a transistor M2, an inductor L1, a diode D4, and a capacitor C6. The input terminal VIN of the voltage controller 231 is coupled to the isolated voltage generator 220 to receive the driving signal Vo, and the adjustment signal terminal ADJ of the voltage controller 231 receives the adjustment signal Dim. The voltage controller 231 adjusts the voltage of its drive output terminal NDRV according to the adjustment signal Dim.

The gate of the transistor M2 is coupled to the driving output terminal NDRV of the voltage controller 231. The source of the transistor M2 is coupled to the second ground voltage, and the drain of the transistor M2 is coupled to one end of the inductor L1. The transistor M2 determines whether or not to conduct according to the voltage of the driving output terminal NDRV of the voltage controller 231. The other end of the inductor L1 is coupled to the LED array 50. The diode D4 is coupled between the isolated voltage generator 220 and the drain of the transistor M2. The current controller 230 can be implemented by a voltage adjustable regulator, which determines the current of the current i _L flowing through the LED array 50 according to the voltage of the driving output terminal NDRV according to the adjustment signal Dim.

FIG. 3A is a schematic diagram of a system of a dimming circuit according to another embodiment of the present invention. Please refer to FIG. 2A and FIG. 3A , except that the dimming circuit 300 includes a pulse width detector 310 . The pulse width detector 310 is coupled to the isolated voltage generator 220 to detect the pulse width of the driving signal Vo. Moreover, the pulse width detector 310 generates an adjustment signal Dim according to the pulse width of the driving signal Vo to adjust the current flowing through the LED array 50 through the current controller 230.

3B is a circuit diagram of the dimming circuit of FIG. 3A. Please refer to FIG. 2B and FIG. 3B, which differ in the pulse width detector 310. The pulse width detector 310 is coupled between the first end 224a of the secondary side 224 of the transformer TR1 and the current controller 230. Since the pulse width of the driving signal Vo is close to the pulse width of the modulation signal Vac', the pulse width detector 310 can know the pulse width of the modulation signal Vac' by detecting the pulse width of the driving signal Vo. Then, the current magnitude of the current i _L flowing through the LED array 50 is adjusted according to the pulse width of the modulation signal Vac'.

3C and 3D are waveform diagrams of the modulation signal Vac', the driving signal Vo, and the current i _L of the dimming circuit of FIG. 3B. Referring to FIG. 3B and FIG. 3C, when the dimming phase angle of the phase dimmer 210 is increased, the pulse width of the modulation signal Vac' is narrowed, and the pulse width of the driving signal Vo is correspondingly narrowed. . When the pulse width of the drive signal Vo is narrowed, the pulse width of the current i _L flowing through the LED array 50 is also narrowed. Moreover, the pulse width detector 310 generates an adjustment signal Dim corresponding to the pulse width of the modulation signal Vac' to control the current controller 230 to reduce the current magnitude of the current i _L flowing through the LED array 50. Therefore, the average current flowing through the light-emitting diode series 50 is lowered, so that the luminance of the light-emitting diode series 50 is darkened.

Referring to FIG. 3B and FIG. 3D, when the dimming phase angle of the phase dimmer 210 is lowered, the pulse width of the modulation signal Vac' is widened, and the pulse width of the driving signal Vo is correspondingly widened. When the pulse width of the drive signal Vo is widened, the pulse width of the current i _L flowing through the LED array 50 is also widened. Moreover, the pulse width detector 310 generates an adjustment signal Dim corresponding to the pulse width of the modulation signal Vac' to control the current controller 230 to increase the current of the current i _L flowing through the LED array 50. Therefore, the average current flowing through the light-emitting diode series 50 is increased, so that the luminance of the light-emitting diode series 50 is brightened. Thereby, the dimming circuit 300 can dim the LED series 50 and increase the range of dimming by adjusting the pulse width and current of the current.

3E is another circuit diagram of the dimming circuit of FIG. 3A. Please refer to FIG. 3B and FIG. 3E , the difference is that the pulse width detector 310 includes a diode D5, a capacitor C7 and a resistor R6. The diode D5 is coupled between the first end 224a of the secondary side 224 of the transformer TR1 and the first end of the capacitor C7. The second end of the capacitor C7 is coupled to the second ground voltage. Resistor R6 is connected in parallel Rong C7. When the modulation signal Vac' forms a pulse wave, energy is transmitted through the transformer TR1 to charge the capacitor C7, so that the voltage of the capacitor C7 is maintained at a voltage value.

When the modulation signal Vac' does not form a pulse wave, the transformer TR1 has no energy to be transmitted, and at this time, the capacitor C7 is discharged through the resistor R6, causing the voltage of the capacitor C7 to approach the second ground voltage. According to the above, the voltage of the capacitor C7 is maintained at a voltage value when the modulated signal Vac' forms a pulse wave, and is maintained close to the second ground voltage when the modulated signal Vac' does not form a pulse wave, that is, the voltage of the capacitor C7. A pulse wave is formed according to the modulation signal Vac', and the pulse width of the voltage of the capacitor C7 is close to the pulse width of the modulation signal Vac'. The voltage of the capacitor C7 is output to the current controller 230 as the adjustment signal Dim.

In addition, the current controller 230 may count when the adjustment signal Dim forms a pulse wave, thereby converting the pulse width of the adjustment signal Dim into a digital value. Then, the current controller 230 adjusts the current of the current flowing through the LED array 50 according to the digital value.

FIG. 3F is still another circuit diagram of the dimming circuit of FIG. 3A. Please refer to FIG. 3E and FIG. 3F , except that the pulse width detector 310 further includes a capacitor C8 and a resistor R7. The resistor R7 is coupled between the first end of the capacitor C7 and the current controller 230. The capacitor C8 is coupled between the current controller 230 and the second ground voltage. The capacitor C8 and the resistor R7 can be regarded as a low pass filter (LPF) for converting the voltage pulse of the capacitor C7 into a DC voltage as the adjustment signal Dim. Then, the current controller 230 adjusts to flow through the LED array 50 according to the DC voltage. The current current of the current.

FIG. 4 is a schematic diagram of a system of a dimming circuit according to still another embodiment of the present invention. Please refer to FIG. 3B and FIG. 4 , except that the isolation voltage generator 410 of the dimming circuit 400 includes a voltage stabilization circuit 411 . The voltage stabilizing circuit 411 includes a transistor M3, resistors R8 and R9, and a Zener diode D6. The drain of the transistor M3 is coupled to the rectifier 221, and the source of the transistor M3 is coupled to the anode of the diode D1. The resistor R8 is coupled between the rectifier 221 and the gate of the transistor M3. The cathode of the Zener diode D6 is coupled to the gate of the transistor M3, and the anode of the Zener diode D6 is coupled to the first ground voltage. The resistor R9 is coupled between the source of the transistor M3 and the first ground voltage.

In this case, the Zener voltage of the Zener diode D6 is 5V, and the voltage received by the input terminal VIN of the controller 222 is about 5V minus the voltage between the gate and the source of the transistor M3 minus two. The forward bias of the polar body D1, that is, when the voltage of the modulation signal Vac' is greater than 5V, the voltage received by the input terminal VIN of the controller 222 is maintained at 5V-V _GS -0.7. Since the voltage stabilizing circuit 411 is not coupled to the third side of the transformer TR1, the energy stored by the feedback transformer TR1 can be avoided to the input terminal VIN of the controller 222. In other words, the controller 222 can be prevented from being turned on instantaneously, and the transformer TR1 transmits energy to the diode series 50 when the controller 222 is turned on, causing the diode series 50 to be instantly illuminated.

According to the above description, a dimming method of a light emitting diode can be integrated to be applied to the above dimming circuit 200. FIG. 5 is a flowchart of a dimming method according to an embodiment of the present invention. Referring to FIG. 2B and FIG. 5, it is first detected whether the dimming phase angle of the phase dimmer 210 is changed (step S501). When the dimming phase angle of the phase dimmer 210 is lowered, the pulse width of the modulation signal Vac' is increased. Further, the drive signal Vo increases its pulse width correspondingly to increase the pulse width of the current i _L flowing through the LED array 50 (step S502). When the dimming phase angle of the phase dimmer 210 is increased, the pulse width of the modulation signal Vac' is reduced. Further, the drive signal Vo correspondingly reduces the pulse width thereof to reduce the pulse width of the current i _L of the light-emitting diode series 50 (step S503). The voltage forming the modulation signal Vac' is isolated from the voltage forming the driving signal Vo, that is, the current loop forming the modulation signal Vac' has no common path with the current loop forming the driving signal Vo.

In addition, a dimming method of a light emitting diode can be further integrated to be applied to the dimming circuit 300 described above. FIG. 6 is a flowchart of a dimming method according to another embodiment of the present invention. Please refer to FIG. 5 and FIG. 6 , which are different in steps S602 and S603 . When the dimming phase angle of the phase dimmer 210 is lowered, the pulse width of the modulation signal Vac' is increased. Further, the drive signal Vo increases its pulse width correspondingly to increase the pulse width and current magnitude of the current i _L flowing through the LED array 50 (step S602). When the dimming phase angle of the phase dimmer 210 is increased, the pulse width of the modulation signal Vac' is reduced. Further, the drive signal Vo correspondingly reduces the pulse width thereof to reduce the magnitude of the pulse width of the current i _L of the light-emitting diode series 50 (step S603).

In summary, the isolated voltage generator of the embodiment of the present invention transmits the pulse width of the modulated signal through a transformer having three sides, and adjusts the pulse width of the driving signal according to the pulse width of the modulated signal. . By this, you can separate The current that forms the modulation signal and the current that forms the drive signal. The dimming circuit and the dimming method of the LED of the embodiment of the invention adjust the pulse width and current of the current flowing through the LED array according to the dimming phase angle of the phase dimmer. Thereby, the range of dimming of the light emitting diode can be increased.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the invention, and any one of ordinary skill in the art can make some modifications and refinements without departing from the spirit and scope of the invention. The scope of the invention is defined by the scope of the appended claims.

50‧‧‧Lighting diodes

100, 200, 300, 400‧‧‧ dimming circuit

110‧‧‧ Pulse width detection circuit

120‧‧‧Low-pass filter circuit

210‧‧‧ phase dimmer

211‧‧‧Two-way trigger diode

212‧‧‧Three-pole AC switch

220, 410‧‧‧ Isolated voltage generator

221‧‧‧Rectifier

222‧‧‧ Controller

230‧‧‧ Current controller

231‧‧‧Voltage controller

310‧‧‧ Pulse Width Detector

411‧‧‧Variable circuit

Vac, Vac’‧‧‧ modulated signal

VAC‧‧‧AC voltage

Vo‧‧‧ drive signal

Dim‧‧‧Adjustment signal

TR1‧‧‧Transformer

C1~C8‧‧‧ capacitor

R1~R9‧‧‧ resistor

D1~D6‧‧‧ diode

M1, M2, M3‧‧‧ transistors

L1‧‧‧Inductance

S501~S503, S601, S602‧‧‧ steps of the dimming method according to embodiments of the present invention

FIG. 1A is a schematic diagram of a system of a dimming circuit of a conventional light emitting diode.

FIG. 1B is a waveform diagram of the modulation signal and the load current of FIG. 1A.

2A is a schematic diagram of a system of a dimming circuit according to an embodiment of the invention.

2B is a circuit diagram of the dimming circuit of FIG. 2A.

2C and 2D are waveform diagrams of the modulation signal Vac', the driving signal Vo, and the current i _L of the dimming circuit of FIG. 2B.

2E is a circuit diagram of the phase dimmer of FIG. 2B.

2F is a circuit diagram of the current controller of FIG. 2B coupled to the LED array.

FIG. 3A is a schematic diagram of a system of a dimming circuit according to another embodiment of the present invention.

3B is a circuit diagram of the dimming circuit of FIG. 3A.

3C and 3D are waveform diagrams of the modulation signal Vac', the driving signal Vo, and the current i _L of the dimming circuit of FIG. 3B.

3E is another circuit diagram of the dimming circuit of FIG. 3A.

FIG. 3F is still another circuit diagram of the dimming circuit of FIG. 3A.

FIG. 4 is a schematic diagram of a system of a dimming circuit according to still another embodiment of the present invention.

FIG. 5 is a flowchart of a dimming method according to an embodiment of the present invention.

FIG. 6 is a flowchart of a dimming method according to another embodiment of the present invention.

50‧‧‧Lighting diodes

300‧‧‧ dimming circuit

210‧‧‧ phase dimmer

220‧‧‧Isolated voltage generator

221‧‧‧Rectifier

222‧‧‧ Controller

230‧‧‧ Current controller

310‧‧‧ Pulse Width Detector

Vac, Vac’‧‧‧ modulated signal

VAC‧‧‧AC voltage

Vo‧‧‧ drive signal

Dim‧‧‧Adjustment signal

TR1‧‧‧Transformer

C1~C4‧‧‧ capacitor

R1~R4‧‧‧ resistor

D1~D3‧‧‧ diode

M1‧‧‧O crystal

Claims (25)

An isolated voltage generator is suitable for a light emitting diode dimming circuit, the light emitting diode dimming circuit has a phase dimmer, the isolated voltage generator comprises: a rectifier, receiving the phase dimming a first voltage is modulated by the controller; a controller having a driving output terminal, a feedback terminal and a current detecting terminal, wherein the controller generates a voltage according to the voltage received by the feedback terminal and the current detecting terminal a control signal, and the control signal is outputted by the driving output; a transformer having a primary side, a secondary side and a tertiary side, the first end of the primary side being coupled to the rectifier, the secondary side The first end outputs a driving signal, and the second end of the second side is coupled to a second ground voltage, the third side is coupled between the input end of the controller and a first ground voltage; a control end, a first end and a second end, the control end of the switch is coupled to the drive output end of the controller, the first end of the switch is coupled to the second end of the primary side, the switch The second end is coupled to the current detecting end of the controller a voltage divider coupled between the first end of the third side of the transformer, the feedback end of the controller, and the first ground voltage to provide a voltage division to the feedback of the controller And a first resistor coupled between the current detecting end of the controller and the first ground voltage. The isolated voltage generator of claim 1, further comprising a first capacitor coupled between the first end of the secondary side and the second ground voltage. The isolated voltage generator of claim 1, wherein the voltage divider comprises: a second resistor coupled to the first end of the tertiary side and the feedback end of the controller; The third resistor is coupled between the feedback terminal of the controller and the first ground voltage. The isolated voltage generator of claim 1, wherein the switch is a transistor. The isolated voltage generator of claim 1, wherein the rectifier is a bridge rectifier. The isolated voltage generator of claim 1, wherein the first voltage is an alternating voltage. The isolated voltage generator of claim 1, further comprising a voltage stabilizing circuit coupled to the controller. The isolated voltage generator of claim 7, wherein the voltage stabilizing circuit comprises: a transistor having a first end coupled to the rectifier, a second end coupled to the controller; and a fourth resistor The second resistor is coupled between the second end of the transistor and the first ground voltage; and a diode coupled to the The control terminal of the transistor is between the first ground voltage. A dimming circuit for a light emitting diode includes: a phase dimmer receiving a first voltage for modulating the first voltage according to a dimming phase angle; an isolated voltage generator coupled a phase dimmer for generating a driving signal according to the modulated first voltage to drive at least one light emitting diode, wherein the first voltage is isolated from a voltage forming the driving signal; and a current controller The current controller is configured to: control a current flowing through the light emitting diode according to an adjustment signal, wherein the current controller includes: a voltage controller having an adjustment signal end and a driving output end, the adjusting signal end of the voltage controller Receiving the adjustment signal for adjusting the voltage of the driving output end of the voltage controller according to the adjustment signal; a second switch having a control end, a first end and a second end, and the control end of the second switch And coupled to the driving output end of the voltage controller, the second end of the second switch is coupled to a second ground voltage, and the second switch is determined according to the voltage of the driving output end of the voltage controller An inductive connection between the first end of the second switch and the light emitting diode; and a second diode coupled to the isolated voltage generator and the second switch Between the first ends. The dimming circuit of the light emitting diode of claim 9, wherein the isolated voltage generator comprises: a rectifier coupled to the phase dimmer to receive the modulated first a controller having a driving output terminal, a feedback terminal and a current detecting terminal, wherein the controller generates a control signal according to the voltage received by the feedback terminal and the current detecting terminal, and the driving signal is generated by the driving The output terminal outputs the control signal; a transformer having a primary side, a secondary side and a tertiary side, the first end of the primary side is coupled to the rectifier, and the first end of the secondary side outputs the driving signal The second end of the secondary side is coupled to a second ground voltage coupled between the input end of the controller and a first ground voltage; a first switch having a control end and a a first end and a second end, the control end of the first switch is coupled to the drive output end of the controller, the first end of the first switch is coupled to the second end of the primary side, the first The second end of the switch is coupled to the current detecting end of the controller; a voltage divider is coupled to the first end of the third side of the transformer, the feedback end of the controller, and the first ground Between the voltages, to provide a voltage divider to the feedback terminal of the controller; and a first resistor Between the current detection terminal coupled to the first controller and the ground voltage. The dimming circuit of the light emitting diode of claim 10, wherein the isolated voltage generator further comprises a first capacitor coupled to the first end of the secondary side and the second ground voltage between. The dimming circuit of the light emitting diode of claim 10, wherein the voltage divider comprises: a second resistor coupled to the first end of the third side and the feedback end of the controller ;as well as A third resistor is coupled between the feedback terminal of the controller and the first ground voltage. The dimming circuit of the light emitting diode according to claim 10, wherein the first switch is a transistor. The dimming circuit of the light emitting diode according to claim 10, wherein the rectifier is a bridge rectifier. The dimming circuit of the light emitting diode according to claim 10, wherein the isolated voltage generator further comprises a voltage stabilizing circuit coupled to the controller. The dimming circuit of the light-emitting diode of claim 15, wherein the voltage stabilizing circuit comprises: a transistor having a first end coupled to the rectifier and a second end coupled to the controller; a fourth resistor coupled between the control end of the transistor and the rectifier; a fifth resistor coupled between the second end of the transistor and the first ground voltage; and a first diode And being coupled between the control end of the transistor and the first ground voltage. The dimming circuit of the light emitting diode according to claim 10, further comprising: a pulse width detector coupled to the isolated voltage generator to detect a pulse width of the driving signal, and The adjustment signal is generated accordingly. The dimming circuit of the light emitting diode according to claim 17, wherein the pulse width detector comprises: a second capacitor having a first end coupled to the isolated voltage generator and the current controller, a second end coupled to the second ground voltage, and a sixth resistor coupled in parallel with the second capacitor. The dimming circuit of the light-emitting diode of claim 18, wherein the pulse width detector further comprises: a third capacitor coupled between the current controller and the second ground voltage; And a seventh resistor coupled between the first end of the second capacitor and the current controller. The dimming circuit of the light emitting diode according to claim 9, wherein the current controller is a buck converter or a buck-boost converter. The dimming circuit of the light-emitting diode according to claim 9, wherein the phase dimmer comprises: a three-pole alternating current switch, the first end of which receives the first voltage, and the second end of which is coupled to the An isolated voltage generator; an eighth resistor, the first end of which is coupled to the first voltage; a bidirectional trigger diode coupled between the control end of the three-pole AC switch and the second end of the eighth resistor And a fourth capacitor coupled between the second end of the eighth resistor and the isolated voltage generator. The dimming circuit of the light emitting diode according to claim 9, wherein the first voltage is an alternating voltage. A dimming method for a light emitting diode, suitable for a dimming circuit of a light emitting diode, a phase dimmer of the dimming circuit of the light emitting diode The method is configured to modulate an AC voltage according to a dimming phase angle, and an isolated voltage generator of the dimming circuit of the LED is configured to generate a driving signal according to the modulated AC voltage to drive at least one LED. a current controller of the dimming circuit of the LED to control a current flowing through the LED, the dimming method includes: when the dimming phase angle is lowered, increasing the modulation a pulse width of the alternating voltage, and a pulse width of the driving signal is correspondingly increased to increase a pulse width of a current flowing through the light emitting diode, wherein a voltage of the modulated alternating voltage is formed The voltages forming the driving signals are isolated from each other; and when the dimming phase angle is increased, the pulse width of the modulated alternating voltage is reduced, and the pulse width of the driving signal is correspondingly reduced to reduce the flow. The pulse width of the current through the light-emitting diode. The method of dimming a light-emitting diode according to claim 23, wherein the dimming circuit of the light-emitting diode further comprises a pulse width detector to generate an adjustment according to a pulse width of the driving signal. And a current controller adjusts a current flowing through the light emitting diode according to the adjustment signal. The dimming method of the light emitting diode according to claim 24, further comprising: increasing the current of a current flowing through the light emitting diode when the dimming phase angle is lowered; When the dimming phase angle is increased, the current flowing through the light emitting diode is reduced.